Brake drum



July 16, 1929. v. BENmx 1.720.815

BRAKE DRUM Filed May 2, 3,928

Patented July 16, 1929.

UNITEDASTATES PATENT OFFICE.

VINCENT BENDIX, F CHICAGO, ILLINOIS, ASSIGNOB TO BENDIX BRAKE COMPANY, OF SOUTH BEND, INDIANA, CORPORATION 0F ILLINOIS.v

BRAKE DRUM,

Application led Iay 2, 1928. Serial 110.2745877.'

This invention relates to improvements in automotive structures and more particularly to brake drums.

In the past, brake drums have been made of corrodible material such as irons and steels. As the ferruginous base metal cor- ,rodes, not only does it become unsightly, but

Iit also becomes seriously weakened by reason of the fact that the iron of relatively high tensile strength is replaced by a deposit of iron oxide'which possesses substantially no strength. This corrosion or oxidation is accelerated during use because of the fact that the temperature of the drum is raised by the generated frictional heats. Upon continued use of a brake drum it is found that it tends to distort and loses its initial circular shape. This materially lowers the braking eiciency. The corrosion of the drum, as Will be appreciated, lowers the strength and hence accentuates this distortion.

It is a major object of this invention yto provide a structural 'material particularly well adapted to the manufacture of brake drums which is of a low corrodibility and of a desirable high tensile strength.

Another obJect of this invention is to provide a `brake drum of high strength, low corrodibility and hardness.

Another object is to provide ganovel composite brake structure of a ferruginous ma terial and another metal,

A further object is to provide a brake drum of a ferruginous base metal with which are combined certain other metals which increase the strength and lower the corrosion. v lThe availability, ease of manufacture, and machining, and the relative cheapness of steel, recommends its use in brake drum structures. Ordina steel, however, is relatively easily corrode When used in brake drums it is subjected to constant wettings and corrosion sets in. This, as is known, consists of oxida- 4tion of the iron and, as has been pointed out, -is accelerated by the frictional heats. This corrosion is practically cumulative; in fact the iron which is formed not only .does not provide a protective coating but accelerates subsequent corrosion or oxidation of the underlying body, As intimated hereinbefore 5'0 this corrosion results in a weakened and uni sightly structure.

This disadvantage may be largely cured by manufacturing a drum from chromium, vanadium, zirconium, or other alloy steels. These materials not onl are characterized by extremely low corrodi ility but are also of high tensile strength. As is known the particular characteristics of these structural metals may be Greatly modified by heat treata0 ment. While these materials do present ma.- I jor advantages they are considerably more expensive than the ordinary steel employed.

According to the purpose of this invention, a brake drum may be produced which presents all of the advantages of the alloy-steels and in addition have a desirable luster.=

The invent-ion comprehends the concept of plating or cementing on a ferruginous base a protective metal in such a manner as to improve the strength and yappearance of the drum .and to minimize corrosion of the underlying metal.

The invention is illustrated diagrammaticall in the accompan ing drawing in which:

ig. l is a longtu inal secton of a brake drum embodying the invention.

Fig, 2 is au enlarged detail View of a brake drum having interior and exterior surfaces.

Fig. 3 is an enlarged detail of a further modification.

The advantages of the invention may be secured by electrodepositing a chromium coating on a ferruginous drum. Preferably the drum is first stamped out or cast to the desired shape. -In carrying out the process the base metal object, such as a steel `stam ing,.is made smooth and clean. This may done by any of the established methods, such as butling pickling to remove oxidesfimmer; sion in suitable solvents such as benzine to remove the grease, or electrolytic cleaning. If desired the base m'etal may also be degasified before being subjected to the platlng operation.

The base metal may be immersed in any of the usual electrolytic baths.` These contain trivalent and hexavalent chromium, to-

tion such as the composition, concentration.

and temperature of the electrolyte, current density and shape of the anode may be varied. Because of the relatively poor throwing power of chromium solutions, it is preferable to shape the insoluble anode to conform to the general shape of the cathode. For the present purpose it is highly desirable to secure a hard file coat, since the higher hardness, wear and abrasion resistance of this type of coat are desiderata in brake drum construction.

The importance of the current density in its relation to the crystalline character and adherence of the coat and the depletion of the anodic solution is now well established. This may vary approximately from 4- or 5 to 20 amperes per sq. decimeter of cathode depending on the results desired and the chosen value of the other governing factors. The plating operation is continued at the given temperature until the deposit is built up to the desired thickness, which may range from about .25 to .5 mils.

Chromium has been utilized as a plate on a number of different metal bases. A value of this material resides in the fact that it serves as a protective coating forthe base metal and not only does not readily tarnish but maintains a high luster over a considerable period of time. It is a fact, however, that chromium plated articles are susceptible to a certain type of corrosion. As a general rule the coatings employed are very thin. These coatings, like coatings of nickel, contain small perforations which may l permit the penetration, or permeation of moisture to the underlying ferruginous metal. This iron in contact with moisture Iand oxygen oxidizes or corrodes. While the chromium layer itself is unattacked it may be detached by the rusting of the iron underneath. This disadvantage may be obviated by increasing the thickness of the coat so as to obtain a continuous and unperforated coated surface, Because of the relatively high cost of chromium, however, the deposit is made as thin as is practical.

It will be appreciated that the latig may be limited to the exterior sur ace of the drum; to the exterior surface and the interior surface of the braking flange, or 1t may be extended over the entire inner and outer surfaces. A. drum having a chromium exterior surface and a plated interior braklng flange provides amember which is of desirable low corrodibility and one which is highly resistant to abrasive wear. These interior and exterior chromium platings materially strengthen the drum structure and hence minimizedrum distortion.

`It will be understood that whilethe imcast drum structure.

proved drum has been described as comprising a chromium plated member, the

novel article may be produced by other specic methods. Thus, in lieu of utilizing an electro deposited plate the article may be produced by a chromizing process. In such a method the member to be coated is first thoroughly cleaned and then packed in a container with l(ir-suitable chromizing mixture,such for example as fifty-five parts of chromium powder and forty-five parts of alumina. The containeris then heated in vacuo or in an atmosphere of an inert gas such as hydrogen. It is important that no free oxygen or water vapor be present,since at the high temperatures employed the chromium powder would quickly be vrendered inactive by the formation of a protective lm of oxide. It should be 'remembered that in treating high carbon steel it is necessary first to decarburize the surface which is to be chromized.

The described treatment may be continued for about four hours in the neighborhood of about 13.50 C. During this period the chromium alloys with the iron in such a manner as to cement the coating metal to the base metal. The resulting chromized iron will resist corrosion as well as sherardized iron, and in addition possesses superior tensile and torsional strengths.

Similarly'the major principlesl of the invention may be eii'ectuated by utilizing a In this case the face of the mold maybe covered with a paste comprising powdered ferro-chromium and a suitable binder, as forexample sodium silicate. When the molten metal is poured into themold it alloys to a considerable extent with the chromium facing. In each of the above described methods the chromium, as an outer metal layer, is firmly cemented to the ferruginous base member.

The advantages of the low cost of a thin coating of chromium, or similar relatively non-oxidizable metals, may be combined withthe highly protective features of a thick coating of these metals. One preferred method of accomplishing this as shown in Fig. 3 will serve to indicate the underlying principles of the invention. These advantages may be achieved by treatmg a brake drum, or the material from which a brake drum is to be made, with metallic zinc so as to form a coating of zinc over the outer or exposed surface of the drum. It will be understood, of course, that, if desired, the ,interior surface of the drum may be similarly treated or the treatment localized to any desired area. To cement the zinc and the iron, the iron plate -may be galvanized or sherardized in the well known manner.

In the electrpche'mlcal series zinc is given as electropositwe to iron. This is tantamount to saying that it has a greater solution pressure or tendency to dissolve. Therefore when it is in contact with moisture the zinc becomes the dissolving electrode and the liron the electrode on which deposits are formed. As a result the zinc not only mechanically protects the iron, that is to say forms a protective coating tliereover, but it also provides chemical protection.

The sherardizing or metallic cementation, as has been indicated, may be carried out according to any accepted practice. These methods in general consist in' cleaning the metal to be treated and then packing it in zinc dust Within an air-tight metal drum. The container is then heated' and tumbled. As a general rule blue dust or mixtures of blue dust and zinc oxide are employed. These processes are generally carried out at tem eratures ranging from about 350 to 37 5 the temperatures employed being dependent upon the desired iron content of the alloy and the composition of the zinc dust. For the present use it is preferable that the treatment be continued for a suiiicient period of time so as to insure a substantialy quantity of zinc in the outer coating after diffusion has takenY place. The resulting structure then comprises a composite metallic member made up of iron and a yzinc iron alloy, the outer surface of which has a large percentage `of zinc. lDuring continued use, particularl at high temperatures, the zinc tends to di use through the iron and decreases the concentration of zinc in the outer layer. Since the zinc iron alloy, like the zinc, is anodic to iron, it is necessary only to carry out'the process sufliciently long to insure al zinc content which will adequately protect the iron.

After the ferruginous material has been treated with the zinc so as to form a coating or skin of a zinc alloy, the surface may then be plated with the desired metal of low corrodibility, in the present instance with chromium. This is carried out by the electrodep`osition method.

It will be observed from the description hereinbefore given that the deposited film or deposit of chromium may be very thin and that no great care need be exercised to prevent perforations. If performations do occur they Will have no deleterious effect since, as has been pointed out, the zinc provides electrochemical protection for the iron. If the moisture has access to the zinc coating this may tarnish slightly, but its unsightliness is in no way comparable to that of ironoxide.,

The metal zinc has been described as merely indicative .of a number of specific materials which ma be used. As has been explained, the protective features of zinc depend in part on its electrochemical characteristics;

thus in place of zinc, the iron may be coated with any suitable substance which is electro positive to it and upon which may be formed an adherent coating of the plating metal. Similarly in lieu of chromium, one may employ other metals such as nickel and cadmium which are depositable as lustrous and non-oxidizing films.

While I have described several embodi-y ments of the invention, it is to be understood that these are given purely by Way of example, for since the underlying features may be incorporated in other specific structures, I do not intend to be limited to those described except as such limitations are clearly imposed by the appended claims.-

I claim: 1. A brake drum comprising a ferruginous foundation metal having a cemented coating containing a metal of lower corrodibility than the foundation metal.

2. A brake drum comprising a foundation metal at least one integral surface of which comprises an alloy of the foundationmetal.

3. A brake drum comprising a ferruginous foundation metal at least one integral surface ofwhich comprises an alloy of the foundation metal.

4. A brake drum comprising a foundation metal having cemented to at least one surface afmetal composition oflower corrodibility than the foundationvmetal.

5. A brake drum comprising a foundation metal, the exterior surface of which comprises an alloy of the foundation metal.

6. A brake drum comprising a plurality of cemented metals of differential corrosion characteristics.

7. A brake drum comprising a foundation metal and a braking flange portion ofa harder' metal cemented to the foundation metal.

8. A brake drum comprising a ferruginous foundation metal the exterior surface of which comprises a metallic substance of lower corrodibilit than the foundation metal.

9. A brake rum comprising a foundation metal and a surface therefor, comprising a different metallic substance cemented to the foundation metal.

10. A brake drum comprising a foundation metal and lan integralA braking flange portion of a harder metallicsubstance.

11. A brake drum comprising a foundation metal and a cemented second metal of greater wearresistance than the foundation metal.

12. A com osite.brake drum comprisin a ferruginous oundation metal and a nonerrus surface thereon.

13. A composite brake drum structure comprisin a ferruginous foundation metal and a bra e iiange surface of a harder metallic substance cemented thereon.

14. A composite brake drum structure 17. A brake durm comprising a ferrugi- 10 comprising a ferruginous member surfacedi nous base and an integral braking flange of with anon-ferrous metal. a chromium containing material.

15. A brake drum comprising a ferrugiy 18. A brake drum comprsing'ferruginous 5 nous base having a surface of chromium platfoundation metal having its exterior surface ed thereon. plated with a relatively nonoxidizable metal. 15 16. A brake drum comprising a ferrugi- In testimony whereof, I have hereuntonous base having chromium incorporated signed my name.v therein adjacent the surface. VINCENT BENDIX. 

